Emotional reactions and states, such as fear, are central to adaptive behavior. Inappropriate emotion is a pervasive source and expression of mental and behavioral dysfunction. Although research with non-humans cannot deal directly with mental emotional experience, it can directly elucidate the neurobiological bases of emotional expression and thereby provide a foundation for both preventative and therapeutic approaches to emotional dysfunction in humans. Emotional reactions are based upon an individual's evaluation of his or her sensory experience, yet little is known about the sensory processing of emotion-producing stimuli. Recent studies reveal that when an animal experiences a sound which has fear- producing capabilities, the coding and representation of that fear stimulus is altered; specifically, the auditory cortex becomes "re-tuned" rapidly and in an enduring manner to emphasize the processing of that stimulus. Our long-term objectives are to understand the neural bases of sensory system processing of emotional stimuli and to discover the mechanisms by which emotional stimuli are stored and often resist extinction when reactions to them are inappropriate. The specific goals of this project are to determine how the auditory cortex processes and represents specific information about fear stimuli by neurophysiological determination of frequency receptive fields and basic response area parameters for single cells in the different lamina of the cortex of guinea pigs. Subjects will be trained in two types of tasks, classical conditioning and instrumental avoidance learning, with two types of problems, single toe training and two-tone discrimination training. Thereafter, mechanisms of the fear-based cortical re-tuning will be studied by using microstimulation of an important thalamic input to the cortex, by blockade of NMDA receptors and by a combination of stimulation and NMDA receptor blockade. These findings will provide the firs systematic analysis of how information itself which is specific to fear stimuli is processed and stored in the cerebral cortex.